Greetings friends! I'm going to show you how to make an IB (infinite baffle) subwoofer system. The idea behind this is pretty simple. The subwoofers use the trunk as an enclosure. Their design is similar to the door speakers that use the door cavity as an "enclosure". Why not a typical sealed/ported/bandbass/whatever box? The answer is: SOUND QUALITY! If you've never heard bass from an IB system before, it'll change you forever...there's nothing like the speed, low end extension, and transparency.

Alright...The next question is: What speakers work? Any Image Dynamics driver works very well, JL audio (unless it's their IB series from a few years ago) doesn't. There's TONS of other speakers besides ID that will work, but I thought I'd keep it simple as they're readily available, and sound great!

Let's get to the install! I wanted to get a pair of 15"s installed on the rear deck without doing ANY cutting, or permanent modification to the car. By looking carefully where the inside of the car meets the trunk, and paying attention to what would become the "front" and "rear" of the baffle, I found the edge/lip of the rear deck that I'd need to make the baffle meet up with.

The first thing I did was to remove the rear deck trim, and remove the factory speaker grilles. The smaller circles are where the Audi seat belts go through the rear deck.


I cut out the center of the trim panel.


Trace the Audi grilles onto a piece of wood that will become the new grille, and cut out. Be sure to measure the distance between the factory grilles, and carry those dimensions onto the new grille to ensure proper fitment. Cut out the center, and wrap in grille cloth. Secure to the Audi's trim panel with small screws. (not shown)




There's no great way to show you how I got the shape of this next piece. Start with a rough "maximum" measurement of the baffle. The purpose of this piece is to get the outer edge to line up with where the "front" and "rear" of the baffle will be in the car. Trust me, there's going to be lots of climbing in and out of the trunk to get it perfect. Use a Sharpie and saw off little by little 'till the wood doesn't bend. Once you've got it perfect, flip it over to check the other side of the trunk. If you're lucky, it'll match perfectly. Mark on the car's metal the edge of this test piece on both sides, then measure the distance between. When you trace this piece onto the baffle, ADD in this distance between test fitting boards.


Cut the 3/4" MDF (or whatever thickness you're using), and carefully locate the cutouts for the drivers. As I mentioned before, I didn't want to drill any new holes. I reused the Audi's rear deck mounting bolts, and trim panel screw holes. Notice the 13mm bolt dead center of the baffle. This also formed a better mechanical coupling to the car and its rear deck, resulting in the "system" (subs, baffle, and vehicle) working together, and a VERY rigid baffle. The method I used also allowed for TOP mounting of the drivers, and thus more trunk space.






Seal up EVERYWHERE around the baffle and fill any/all holes that will allow the two sides to "leak". Realize it will never be 100%, but the closer, the better. I used a combination of Dynamat material, and "Great Stuff" - http://greatstuff.dow.com/greatstuff/cons/windoor.htm Use this where the baffle meets the metal, and anywhere "air" from the back side of the board could go into the cabin...remember the trunk is part of the "enclosure" now.

I painted the topside of my baffle black and will re-cover the bottom in Audi matched trunk liner material (not available at time of photos).
Reinstall the rear deck, and attach the grille:



Vacuum the car - not shown in pics.

Cheers,
Matt

 

Holy hell.

 

Thanks Bacon!

Bump for some "closer to finished" pics.

 

What else do you have planned for it?

 

Next I'll show you how I installed the 2 Zapco amplifiers, and 5 farad Alumapro cap. They'll be visible when the seats are folded down, under lexan, and fan cooled to the trunk. Hopefully that'll be done today...

 

I've been a big fan of trunk saving installs for many years, and as long its a quality sub for specific IB application thats been tested (along with the proper separation for the front of the sub from the back, as you said) - sound quality is excelent. Not only you will fell the bass but hear it too. The only draw back in my experience, they tend to be a little more power hungry... My first IB install was in my old Coupe GT with a pair of high end KEF subs, and they sounded incredible!

Good luck with the rest of the install, post some finished pics!

D

 

Some finished pics...

 

The car's currently undergoing a HUGE change...moving up to Expert Class next season.

There aren't any subs in the rear anymore...only a single 12" up front. I've posted pics of that here:

https://www.audiforums.com/m_609575/tm.htm

I'm keeping the McIntosh MX4000 and my own DSP, Arc Audio SE amplifiers...but that's about it...I'll post more pics as the install progresses!